Optical networks are used to deliver data, voice and video services to multiple network subscribers using one or more optical fibers. The optical networks that are used to deliver the data, voice and video services may be either passive or active. In a passive optical network (PON), passive optical components such as optical combiners and splitters enable multiple subscribers to share the same optical fiber. Thus, the PON functions as a point-to-multipoint optical network. A PON may conform to any of a variety of PON standards, including, for example, gigabit-capable PON (GPON) (ITU G.984), gigabit-capable Ethernet PON (GEPON) (IEEE 802.3) and broadband PON (BPON) (ITU G.983). In an active optical network, electrically-powered equipment, such as switches, routers, and multiplexers, is used to distribute the signal to the subscriber premises. Thus, an active optical network, such as an active Ethernet optical network, operates as a point-to-point network.
Optical transceiver modules used in optical networks convert optical signals received via an optical fiber into electrical signals, and convert electrical signals into optical signals for transmission via an optical fiber. In the transmitter portion of a transceiver module, an opto-electronic light source such as a laser performs the electrical-to-optical signal conversion. In the receiver portion of the transceiver module, an opto-electronic light detector such as a photodiode performs the optical-to-electrical signal conversion. A transceiver module commonly also includes optical elements or optics, such as lenses, as well as electrical circuitry such as drivers and receivers. A transceiver module also includes one or more connector receptacles to which an optical fiber cable can be connected. The light source, light detector, optical elements and electrical circuitry can be mounted within a module housing. Various transceiver module configurations are known.
A bidirectional optical transceiver module can employ wavelength division multiplexing (WDM), such as coarse wavelength division multiplexing (CWDM), to achieve provide a transmission channel and a receive channel over a single fiber. WDM techniques are commonly employed in bidirectional optical transceiver modules. The opto-electronics of a WDM bidirectional transceiver module commonly include a laser that emits light of a first wavelength and a photodiode that receives light of a second wavelength. The optics of a WDM transceiver module commonly include one or more bandpass filters that are highly transmissive to some wavelengths and highly reflective to other wavelengths. The light beams are thus communicated along paths that include the one or more filters between the end of the fiber and the laser and photodiode. Due to space constraints and mechanical mounting considerations in the module, these elements can be positioned relative to one another in a manner that results in the optical path having a “zigzag” shape. For this reason, such a technique of implementing CWDM in a transceiver module is referred to as a “zigzag.”
A need exists for a bidirectional optical transceiver module that is well suited for use in PON networks where the transmission and receive channels are separated by a relatively large wavelength difference and in more conventional CWDM networks where the wavelength difference is relatively small and typically affects only the specifications of the filter used in the optics.